Internal combustion engines are ubiquitous in the modern world and used for numerous applications. Internal combustion engines are the most common type of engine utilized for imparting motion to automobiles, propeller-driven aircraft, boats, and a variety of other types of vehicles, as well as a variety of types of motorized work vehicles ranging from agricultural equipment to lawn mowers to snow blowers. Internal combustion engines also find application in numerous types of devices that are not necessarily mobile including, for example, various types of pumping mechanisms, power washing systems, and electric generators.
Many different types of internal combustion engines have been designed and built over the years. Among the most common such engines are engines in which one or more pistons are mounted within one or more corresponding cylinders arranged about a crankshaft, where the pistons are coupled to the crankshaft by way of one or more connecting rods such that linear movement of the pistons is converted into rotational movement of the crankshaft. In terms of automotive engines, typically such crankshaft-based engines are “Otto engines” in which each engine piston repeatedly moves through a series of four strokes (cycles), namely, a series of intake, compression, combustion and exhaust strokes.
Although such conventional, crankshaft-based four stroke engines are popular and are undergoing continuing improvement, such engines nevertheless suffer from several limitations. First, the fuel efficiencies that can be achieved by such engines continue to limited, something which is disadvantageous particularly insofar as the world's supply of fossil fuels is limited, insofar as demand (and consequently price) for fossil fuels continues to increase, and insofar as concerns over the impact of fossil fuel-based internal combustion engines upon the global environment continue to grow. The fuel efficiencies of such engines are limited for a variety of reasons including, for example, the weight of such engines, and frequent operation of such engines in an idling manner when no load power is truly required (e.g., when an automobile is at a stop light). A further factor that limits the fuel efficiencies of many such engines that employ spark plugs in combination with high octane fuels (rather than diesel engines) is that such engines, in order to avoid undesirable pre-ignition combustion events during the compression strokes of such engines, are restricted to designs with relatively modest (e.g., 9-to-1 or 10-to-1) compression ratios.
Second, because combustion strokes in such engines only occur during one of every four movements of a given piston, such engines by their nature require that an external input force/torque be applied to impart initial rotational momentum to the crankshaft of the engine in order for the engine to attain a steady state of operation in which the engine (and its crankshaft) is naturally able to advance to successive positions at which combustion events can take place. For this reasons, such engines typically employ an electrically-driven starter motor that initially drives the engine until the engine is able to attain its own steady state of operation. Relatedly, to maintain such steady state rotational operation, and also to reduce the degree to which output torque provided by the engine varies as combustion events occur and then pass, such engines typically require a flywheel that tends to maintain the rotational momentum of the engine at a constant level.
Although such starter and flywheel components employed in conventional crankshaft-based four stroke internal combustion engines are commonly used, and well-understood in terms of their operation, the inclusion of such devices within such engines adds complexity and/or significant weight (as does a crankshaft) to the engine that, consequently, can increase the cost of designing or building the engine, increase the complexity of maintaining or repairing the engine, and/or further reduce the fuel-efficiency of the engine. Further, depending upon how effective the starter of the engine is in terms of starting the engine, the need for a starter can further be an impediment to effective (and enjoyable) operation of the engine. For example, it can be particularly frustrating to an operator when a starter mechanism fails or otherwise is incapable of starting an automobile engine in a short amount of time, particularly when the operating environment is cold such as during wintertime.
Various other types of internal combustion engines likewise suffer from various limitations that may be the same, similar to, or different from the limitations described above. For example, while many of the above-described crankshaft-based 4 stroke internal combustion engines are able to run fairly cleanly in terms of their engine exhaust emissions, in contrast many diesel engines as well as conventional crankshaft-based 2 stroke engines under at least some operating circumstances are unable to effectively combust all of the fuel that is delivered into the cylinders of those engines and consequently emit fairly high levels of undesirable exhaust emissions. This is problematic particularly as there continues to be increasing concern over environmental pollution, and various governmental entities are continuing to enact legislation and regulations tending to require that such engine exhaust emissions be restricted to various levels. Such crankshaft-based engines also still require starters and flywheel mechanisms to allow for starting and proper operation of the engines.
Although most conventional internal combustion engines employ a piston-driven crankshaft, other designs for internal combustion engines have also been developed. It is known, for example, to construct an engine in which the linear motion of pistons is transformed into rotational motion at an engine output not by way of connecting rods and a crankshaft, but rather by way of utilizing the pistons to drive hydraulic fluid toward a hydraulic motor that rotates in response to receiving such hydraulic fluid. Yet even this type of engine can suffer from some of the same types of limitations described above. In particular, such engines typically also are limited in their efficiency, and/or require additional components such as a starter and/or flywheel in order to allow the engine to begin running in a steady-state manner, and to continue running in such a manner.
For at least these reasons, it would be advantageous if an improved internal combustion engine could be developed that did not suffer from one or more of the above-described limitations to as great a degree. In particular, it would be advantageous if, in at least some embodiments, such an improved internal combustion engine was capable of operating in a more fuel-efficient manner than some or all of the above-described conventional engines. Further, it would be advantageous if, in at least some embodiments, such an improved internal combustion engine could be designed to operate in such a manner that one or more commonly-employed components (e.g., a starter or a flywheel) were not needed.